Cartoon of charge and discharge in the dual carbon battery. Source: Power Japan Plus. Click to enlarge.

The Power Japan Plus cell is based on the work of Professor Tatsumi Ishihara at Kyushu University in Japan; Power Japan Plus will continue developing the dual carbon battery technology in partnership with Prof. Ishihara and the university. In a 2013 patent filing on the technology, Ishihara and his colleagues explain the charge and discharge reactions thusly, using a LiPF₆ salt (as did Seel and Dahn):

Positive electrode: PF₆⁻ + nC ⇄ C_n(PF₆)+e⁻

Negative electrode: Li⁺ + nC+e⁻ ⇄ LiC_n

→ charging reaction; ← discharge reaction

Discharged capacity is determined by the anion storage capacity of the positive electrode; the amount of possible anion release of the positive electrode; the cation storage capacity of the negative electrode; the amount of possible cation release of the negative electrode; and the amount of anions and cations in the non-aqueous electrolyte.

US Army researchers develop their own dual-graphite battery
In a recent paper in the RSC journal Energy & Environmental Science, a team from the US Army Research Laboratory reported a reversible dual-graphite intercalation chemistry with simultaneous accommodation of Li+ and PF6− in graphitic structures using a high voltage electrolyte based on a fluorinated solvent and additive, which is capable of supporting the chemistry at 5.2 V with high efficiency.
This all-graphite battery promises an energy storage device of low cost, high safety and high environmental friendliness that are critical for large scale energy harvesting/storage needs, that team concluded.

To improve the discharged capacity in the dual carbon cell, it is necessary to increase not only the positive-electrode active material and the negative-electrode active material but also the amount of the non-aqueous electrolyte including a lithium salt. Because the ion concentration of the electrolyte changes during cycling, there must be enough electrolyte salt in the cell to guarantee conductivity, and there must be enough solvent to enable the salt to be disolved at any state of charge or discharge.

In their patent filing, Ishihara and colleagues note that in such a dual carbon cell, precipitation and dissolution of a lithium salt as a supporting salt may take place at any location in the cell where a non-aqueous electrolyte exists. However, precipitation of a large amount of the supporting salt on electrode surfaces causes a problem of decreased power density of the cell because the supporting salt in a solid state is an insulator.

Prof. Ishihara and his team claim, among other things, that they have devised a way to prevent the supporting salt from precipitating on an electrode surface, along with improved high discharged capacity and improved gravimetric energy density.

Power Japan Plus says that its battery charges 20 times faster than lithium ion batteries; is rated for more than 3,000 cycles; and can slot directly into existing manufacturing processes, requiring no change to existing manufacturing lines.

The ability to charge the battery so rapidly could, the company proposes, enable longer-range electric vehicles, as regenerative breaking will be more efficient. Because the dual carbon battery can be 100% discharged, it can further extend the length of each usable charge cycle, the company also suggests.

Power Japan Plus will begin benchmark production of 18650 Ryden cells later this year at the company’s production facility in Okinawa, Japan. This facility will allow the company to meet demand for specialty energy storage markets such as medical devices and satellites. For larger demand industries, such as electric vehicles, Power Japan Plus says it will operate under a licensing business model, providing technology and expertise to existing battery manufacturers to produce the Ryden battery.

Resources

• Jeffrey A. Read, Arthur V. Cresce, Matthew H. Ervin and Kang Xua (2014) “Dual-graphite chemistry enabled by a high voltage electrolyte” Energy Environ. Sci. 7, 617-620 doi: 10.1039/C3EE43333A

• Onagi et al. (2013) US patent application 20130288113: Non-aqueous electrolyte storage element

• S. Rothermel, G. Schmuelling, O. Fromm, P. Meister, H.-W. Meyer, T. Placke, M. Winter (2013) “Challenges and opportunities of dual-graphite cells based on ionic liquid electrolytes,” ECS 224, #891

• Tatsumi Ishihara, Yuji Yokoyama, Futoshi Kozono, Hidemi Hayashi (2011) “Intercalation of PF₆^- anion into graphitic carbon with nano pore for dual carbon cell with high capacity,” Journal of Power Sources, Volume 196, Issue 16, Pages 6956-6959

• Tatsumi Ishihara, Yuji Yokoyama, and Shintaro Ida (2010) “Intercalation of PF₆^- anion into Graphitic Carbon with Nano Pore for Dual Carbon Cell with High Capacity,” IMLB 15 #224

• J. A. Seel and J. R. Dahn (2000) “Electrochemical Intercalation of  PF ₆ into Graphite” J. Electrochem. Soc. vol. 147, issue 3, 892-898 doi: 10.1149/1.1393288

• Carlin, R. T.; Delong, H. C.; Fuller, J.; Trulove, P. C. (1994), “Dual Intercalating Molten Electrolyte Batteries” Journal of the Electrochemical Society141, (7), L73-L76 doi: 10.1149/1.2055041

• McCullough, F. P.; Levine, A.; Snelgrove, R. V., U.S. Pat. 4,830,938 1989